Electronic nose

Oliver Tomic

Analysis of odor and flavor in food has traditionally been performed either by a trained sensory panel or by head-space gas chromatography mass spectrometry. These methods are time consuming and costly and there is a need in the food industry for objective automated non-destructive techniques that can characterize odor and flavor in food.

Content in this page:
1. Electronic nose facts
2. Applications and research
3. Cooperation and development
4. Publications Electronic Nose (at Campus Ås)
5. Contacts and related links

1. Electronic nose facts
Introduction
New methods should allow a high number of samples to be analyzed within a short period of time with a sufficient reproducibility and accuracy. During recent years there has been a rapid development of a concept named electronic nose (artificial nose) based on chemical gas-sensor array technology which seems to fulfill these requirements.

Gas sensor technology and data analysis
With the term Electronic Nose is understood an array of chemical gas sensors with a broad and partly overlapping selectivity for measurement of volatile compounds within the headspace over a sample combined with computerized multivariate statistical data processing tools (Gardner and Bartlett, 1994). The sensor array of an electronic nose has a very large information potential and will give a unique overall pattern of the volatile components.
Several commercial gas sensor array instruments are now available on the market covering a variety of chemical sensor principles, system design and data analysis techniques. A series of different detection principles can be used in chemical gas sensors: heat generation, conductivity, electrical polarization, electrochemical activity, optical properties, dielectric properties and magnetic properties.

By chemical interaction between odor compounds and the gas sensors the state of the sensors is altered giving rise to electrical signals which are registered by the instrument analogue with the secondary neurons. In this way the signals from the individual sensors represent a pattern which is unique for the gas mixture measured (Fig. 1) and is interpreted by multivariate pattern recognition techniques like artificial neural network, the brain of the instrument. Samples with similar odorous generally give rise to similar sensor response patterns and samples with different odorous show differences in their patterns. When the sensor patterns for a series samples are compared, differences can be correlated with the perceived sample odor. The sensors of an electronic nose can respond to both odorous and odorless volatiole compounds. In principle, the electronic nose can be applied to any product that gives off volatiles with or without smell provided that this occurs within the sensitivity range of the sensors.

The data processing of the multivariate output data generated by the gas sensor array signals represent another essential part of the electronic nose concept. The statistical techniques used are based on commercial or specially designed software using feature extraction and pattern recognition routines like principal component analysis (PCA), partial least squares (PLS), functional discriminant analysis (FDA), cluster analysis, fuzzy logic or artificial neural network (ANN). Other newer techniques that seem to have an interesting potential are multiway decomposition and independent component analysis (ICA).

Food Applications
In principle, the results obtained from a gas-sensor array represent qualitative and quantitative information of the composition of the headspace gas mixture of a sample. The technique should therefore have a great potential in a number of applications related to food. Numerous electronic nose studies related to food already have been published. Many of them represent preliminary feasibility studies, but a limited number of them represent basic studies including long term validation of the technique on a specific application.

Electronic noses have great potential are the following areas:
· Odour analysis
· Lipid oxidation
· Freshness and spoilage
· Taints and off-flavour
· Food safety
· Process control
· Packaging

Perspectives
The electronic nose technology applied on food must be regarded as being in its early stage. So far, the applications in the scientific literature seem promising for future use in the food industry. There is a rapidly advancing research and development going on both on sensors and instrument hardware and software in order to enhance selectivity, sensitivity and reproducibility of the gas sensors. Much effort is also put into solving the drift problem of the sensors by increasing the stability and life-time of the sensors. There is also carried out research in order to develop improved mathematical algorithms for drift counteraction, automatic calibration and standardization and transferability between gas sensor array instruments. At the same time development of different applications by the industry and research centers in different fields is proceeding.

On-line sensors play a key role in the automation of food control and processing. In near future when the basic issues of the gas-sensors have been solved, we will see more on-line gas-sensors implemented in the industry. For each application, however, technical problems have to be solved for implementation on-line. One interesting vision for the future would be to have a fully automated platform of different kind of sensors to monitor the essential information required for the characterizing of quality of the raw material, process or product. Gas-sensors would make up a vital part of such a multi-sensor system. This may be realized in the food industry in the near future.


2. Applications and research
Presently, the electronic nose group at Matforsk is focusing its research using electronic noses in the following areas:

- Monitoring and analysis of different fermentation processes
- Determination of fish quality (development of a ”fish-nose”)
- Data transfer between instruments and data standardization
- Drift compensation
- Application and testing of various statistical methods for improved explotation of raw data

Ph.D. student(s): Oliver Tomic
Title: Gas-sensor array measurement technique. Signal processing and quality analysis of food


3. Cooperation and development:

MATFORSK had over a period of 7 years a close cooperation with NST (Nordic Sensor Technologies, Sweden), a former manufacturer of commercial instruments. During this period MATFORSK contributed with its expertise in food science and its status as an advanced user to improve technique and usability of NST’s instruments. Two years ago, NST has merged with MoTech, another manufacturer of electronic noses from Germany, to form AppliedSensor. The new company now solely concentrates on development and production of gas-sensors and has abandoned manufacturing of complete electronic nose instrument with all mechanics around the gas-sensors.

MATFORSK is now part of an EU-project for the development of a ”fish nose”, an electronic nose that is tailored for applications with focus on fish as the main product. The project will last from 2002 until 2005 and will be financed with 1.4 million €. MATFORSK will contribute to the development with its experience from the previous cooperation with NST and its expertise in food science.



Updated: 18.11.02
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